Stability of lorazepam diluted in bacteriostatic water for injection at two temperatures

Lorazepam is commonly used to produce sedation in infants. As errors may occur with the measurement of small volumes of concentrated drugs, we studied the stability of lorazepam diluted from 4 mg/ml to 1 mg/ml in bacteriostatic water for injection at two temperatures. The diluted lorazepam was stored in 10 glass vials (five at 22 degrees C and five at 4 degrees C). Samples were collected at 0, 7, 14, 28, 42, 56, 70 and 91 days after storage at each temperature. Lorazepam was measured in duplicate from each of five vials (n = 10) at each temperature by a specific and stability-indicating high-performance liquid chromatographic (HPLC) method. After 7 days' storage, the mean lorazepam concentration was 88% of the original concentration at 22 degrees C, and 90% of the original concentration at 4 degrees C. After 2 weeks of storage, the mean lorazepam concentration was 42% of the original concentration at 22 degrees C, and 1.5% of the original concentration at 4 degrees C. Crystals appeared after 4 weeks of storage at 22 degrees C and after 2 weeks of storage at 4 degrees C. At 3 months the mean lorazepam concentration was 6.1% and 7.5% of the original concentration at 22 degrees C and 4 degrees C, respectively. Thus, lorazepam diluted in bacteriostatic water for injection and stored in glass vials is stable for less than 7 days at 22 degrees C and for 7 days at 4 degrees C.